Cutting tool



10 shee 1 w. M. BURA CUTTING TOOL IHH H'..".."

W E Q W. M, TTING T0 pril 4, 1950 0 Sheets-s 2 Original. Filed March 31. 1941 llll 'lllll illllllll llllllllll .fiiiiiiiiiiin:

OR. gg Zara, KC TOkNfy w. BURA cu'r'rmc TOOL April 4, 19 50 10 Sheets-Sheet 3 ori inal Filed ll'arch :51. 1941 INVENTOR. Walk) Mar]? Zara a? a M a? C.

'47 OR/VEYS w. M. BURA cu'r'rmc TOOL April 4, 1950 10 Sheets-$11691. 4

Original Filed Karen 31, 1941 INVENTOR. {Va/fer iar/1i Bura 7 t t 25 HTTORNEXS w. M BURA cu'r'rms TOOL April 4, 1950 1o Shqet-Sheet 5 Original Filed March 31 1941 INVENTOR. Waller Iva/r113 Bard BY 4 AM ATTORNEY:

April 4, 1950 I w. M. BURA 2,502,922

cu'r'rms TOOL Origi al Filed March :51. 1941 1o Sheets-Sheet s INVENTOR. BY 7 /21- Mar/KB April 1950 w. M. BURA 2,502,922

' cu'n'mc TOOL Original Filed March 31. 1941 i 1o Sheets-Sheet v c. M 3c ATTORNEYS pril 4, 19 w. M. 2,502

cu'r'rm iginal File 0 Sheets-She INV /r zum BY a v 6 c M fin E w. M. BURA cu'r'rmc TOOL April 4; 1950 10 Sheets-Sheet 9 Original Filed March 31. 1941 INVENTOR.

April 4, 1950 w. M. BURA 7 cum-1m TOOL Original Filed March 31, 1941 '10 Sheets-Sheet 10 1 .21 g 0mm FEED PEI? If m ou/r/o/v 0 EEO f=0l00lh K perrev. film/6E car 01? E Far/m r001 Q l i k; .SP/RflZLEflD A: 00. 0F u w wow \L/HNGLE [30mm E 1.10) rev. 1 t \1 k -1 .025111 I perrea 5 3010 Q 5 4 .2 z i i m FEED 05 mm mmvrm Val/0 flax/f jam BY 4 Q za f Patented Apr. 4, 1950 CUTTING TOOL Walter Mark Bura, Orange, N. 1., minor to Norton Company, Worcester, Mass a corpora-' tion of Massachusetts Application April 28, 1941, Serial No. 390,521, now Patent No. 2,375,819, dated May 8, 1945, which is a continuation of application Serial No. 386,177, March 31, 1941. plication November 1, 1944, Serial No. 561,437

2 Claims.

which tools in many cases must also be formed with very accurate contours (as viewed for example from above). It is necessary in most cases to provide different angles of clearance at the forward end of the tool from those on the sides, as viewed in vertical planes normal to the cutting edges at the points in question. Thus the clearance angle in the direction of feed must be greater than those in a direction perpendicular to the direction of feed.

In most instances the corners of the cutting tool are rounded, the radius of curvature of the rounded corner corresponding to the requirements of the particular .use to which the tool is to be put, said radius being constant or varying. It will be readily understood that if the angle of clearance at the front of the tool, viz., at the point where the rounding begins, is different from the angle of clearance at the side of the tool, viz., where the rounding ends, it will be necessary gradually to change the angle of clearance (as seen in a vertical cross-section taken along the radius of curvature at the point in question) from one extremity of the rounded corner to the other. No method for forming such a tool has heretofore been known.

It is an object of the present invention to provide a cutting tool in which the angle of clearance, as viewed in vertical planes normal to the cutting edge at the points in question, is gradually changed from one portion of the tool to another.

Another object is to provide a tool having at at least one rounded corner, the form of the corner being such that the clearance angle in a vertical plane in the direction of feed of the so Divided and this ap- 2 tool is identical or substantially identical at all points around said rounded corner.

Another object is to form a cutting tool with a cyclonoid surface as hereinafter defined.

1 nother object is to provide a plurality of such tools of identical contour through the use of a controlling pattern.

These and other objects and advantages of this invention will be apparent from the following specification and the accompanying drawings of several possible illustrative embodiments of the invention, in which drawings:

Fig. 1 shows a side elevation of one form of apparatus for grinding such tools showing the position of the parts while a controlling pattern is being formed;

Fig. 1a is a partial view similar to Fig. 1 but showing a modification;

Fig. 2 is a partial side elevation partly in section showing the machine of Fig. 1 in the act of grinding a tool under the -control of a controlling pattern;

Fig. 3 illustrates a. front elevation of said illustrative machine partly in section;

Fig. 4 is a side elevation partly in section showing the grinding wheel dresser in position for use;

Fig. 5 is a fragmentary top view of a part of the machine shown in Fig. 2 viewed on the line 5-5 of Fig. 2;

Fig. 6 is a similar section viewed on the line 66 of Fig. 2;

Fig. 7 is a rear view of the tool holder shown in Fig. 1 and Fig. 2;

Fig. 8 is a perspective of a bevel plate of the type which may be applied to the top of the work table when it is desired to change the eflfective angle thereof;

Fig. 9 illustrates a bevel plate which may be used under the tool holder of Fig. 7 for the purpose of varying the side clearances to be applied to the tool;

Fig. 10 shows a modified form of tool holder in which the tool may be adjusted around its longitudinal axis to vary the clearance to be applied to the sides of the tool;

Fig. 11 shows a modified form of the tool holder illustrated in Figs. 1, 2, '7, and 10, means being provided for varying the angle of back rake to be applied to the tool;

accepts Fig. 12 shows a partial side view of a typical tool formed according to the present invention; Fig. 13 is a view of the top of such a tool;

Fig. 14 is a front view thereof;

Fig. 15 is a partial view mostly in vertical section showing a modification in which the table is pivoted for ready adjustment;

Fig. 16 is a plan view of the machine as it may appear when provided with the pivoted table shown in Fig. 15;

Fig. 17 is a view similar to Fig. 13 of a tool having a somewhat different profile and ground with the table slope angle at zero, as shown in Fig. 15;

Fig. 18 is a longitudinal vertical cross-sectional view taken along the line I3-ll of Fig. 17;

Fig. 19 is a view similar to Fig. 18 taken on theline l2l2ofFig. 17;

Fig. 20 is a similar view taken on the line 23-20 of Fig. 17;

Fig. 21 is a plan view of a form of turning tool embodying the invention;

Fig. 22 is a vertical cross-sectional view of the tool of Fig. 21 taken on the line 22-22 of Fig. 21;

Fig. 23 is a vertical cross-sectional view of the tool of Fig. 21 taken on the line 23--23 of Fig. 21;

Fig. 24 is a plan view of a form of plunge-cut tool embodying the invention shown in connection with a work piece upon which it is operating;

Fig. 25 is a plan view of a form of facing tool embodying the invention shown in connection with a work piece upon which it is operating;

Fig. 26 is a plan view of a form of finish facing tool embodying the invention shown in connection with a work piece upon which it is operating;

Fig. 27 is a plan view of a form of cut-oi! tool embodying the invention shown in connection with a work piece upon which it is operating;

Fig. 28 is a plan view of a form of boring tool mounting the invention shown in connection with a part being bored;

Fig. 29 is an elevation of a planer or shaper tool madein accordance with the invention shown in connection with a work piece upon which it is operating;

Fig. 30 is a plan view of a form of turning tool' similar to Fig. 21, but showing a tool whose left cutting edge is inclined to the axis of the tool;

Fig. 31 is a cross-section of a work piece showing the path of a plunge-cut or facing toolrelative to the work;

Fig. 32 is a chart showing graphs indicating the theoretically necessary relief angles on tools for various minimum work diameters and various feeds per revolution;

Fig. 33 represents the drawing of a work piece having certain dimensions, together with a tool set-up capable of producing said workpiece;

Fig. 34 is a radial view of an inserted-bit radialmilling cutter;

Fig. 35 is an axial view of the cutter shown in Fig. 34;

Fig. 36 shows an inserted-tool axial-milling cutter or fly-cutter; and

Fig. 37 is an axial view thereof.

Referring to said drawings, the symbol TB indlcates a typical tool bit made in accordance with the invention. Referring to Figs. 12, 13, and 14, it will be noted that the front clearance or relief angle is designated by a, the left side clearance angle by b, the right clearance angle by c, and the back rake angle by a. The angle of slope of the bottom of the tool relative to thebottom of the tool holder is indicated by I (Figs. 2 and 11) In the form of embodiment selected to illustrate the invention, as shown in the drawings, the numeral I 0 designates a base preferably formed hollow, as shown, and having a front wall II and an intermediate wall l2 and having a rearward extension I3 upon which is mounted a motor l4 firmly fixed thereon as by bolts II. The forward portion of the base is shown as provided with a top It, formed with suitable ways such as guide grooves II adjacent each end, these grooves extending from the front of the housing toward its rear. Upon said housing is supported a carriage it being slidably mounted relative to the base as by ribs l9 fitting in said grooves ll. The upper face 20 of the carriage or bed plate i8 is usually sloped downwardly from rear to front. In the particular form illustrated. this slope is selected as 1 /2. This slope determines the side clearance angles imparted to the tool and contributes to the determination of the and clearance angle as will be explained hereinafter.

Any suitable means may be provided to shift the table II forwardly and rearwardly upon the base, viz., with respect to the grinding wheel. In the form illustrated the upper part of the wall II is provided with a bore or opening 2| the front end of which is enlarged as at 22 and in this opening is fitted a correspondingly shaped bushing 22. In the upper part of the wall l2 and axially aligned with the bore 2| is a bore 24 having an enlarged rear end 2|. In the bore 24 is fitted-a bushing 23. A feed screw, indicated in general at 21, is provided at its front end with a journal 23 fitting the bushing 23 and at its rear end with a journal 23 fitting the bushing 26. The rear end of the feed screw has a flange portion 34 which fits the bore portion 25 so that the feed screw is held from forward movement. This feed screw has a reduced and threaded portion 3| projecting forwardly from the Journal 23 and upon which projection is mounted a graduated washer or dial indicator 32 which rests against the front face of the wall I I. A crank handle 33 is screwed on the end 3| and bears against the washer 32 which, being of greater diameter than the bore 22, prevents rearward movement of the screw. A key 34 serves to prevent rotation of the parts 32 and 33 on the feed screw after these parts have been assembled and properly adjusted. An index point 35 is scribed on the wall l2 to cooperate with the graduations of the washer 32. Secured to the under side of the forward portion of the carriage i3 is a nut 36 which engages the threaded portion 31 of the feed screw 21. Thus rotation of the crank 33 will cause movement of the carriage in the desired direction on the housing.

The rear edge of the carriage I3 is recessed as at 33 and in the recess is fixed a bar 22 formed rithzan abutment ledge 42 extending above the ace The motor l4 has a shaft 4| on the front end of which is mounted a material removing device such as a cup-shaped grinding wheel 42 having an annular grinding face 43. This grinding wheel has its forward portion revoluble in the recess so that, by manipulation of the feed screw, the abutment ledge 40 may be adjusted with respect to the grinding face 43. A suitable support such as an arch frame 44 has its ends secured to the carriage is at each side of the recess 32 as by bolts 43. This arch frame extends over the wheel 42 and, centrally above the wheel, is provided with a boss 43. A block 41, comprising a controlling pattern grinding block, has its front face accurately formed as a plane surface and is fixed to the boss by screw 43. The front face of this block 41 lies somewhat to the rear of and parallel to the grinding face 43.

I When a pattern is to be ground there is removably mounted on the carriage l8 a. spacer or step block 49, which is properly positioned when in use by dowels 50 fitting in dowel holes II in the carriage It. This spacer is recessed at 52 to embrace the front upper part of the wheel 42 and its upper face 53 is in the form shown inclined 1 from the horizontal so as to lie parallel to the face 20 when the spacer is in position. Any other suitable holding means may be used to hold the parts l8 and 49 in properly adjusted relation.

A tool holder is indicated in general at 54 and has an accurately formed plane under surface 55 to rest and slide or turn on either of the surfaces 20 or 53. This box 54 has at its lower forward end an extension 56 which is provided on its under side with a rearwardly opening recess 51. In this recess is mounted a controlling pattern 58 which projects rearwardly of the tool holder and is secured and positioned accurately thereto by the screw 59 and dowels 60. In Fig. 1 there is shown a master form 6| which may represent either a tool which is to be reproduced as will be presently explained, or other suitable master pattern such as a template. The tool holder is arranged in the form shown to hold the bottom face of tools to be ground, or the master tool or master pattern to be followed, at an angle of 8% to its bottom face. Screws 63 are employed to hold the tool in place.

On the boss 46 is provided a bearing boss 64 having anti-friction bearings 65 at each end of an opening. In these bearings is mounted a shaft 51 on the front end of which is fixed an arm 66 carrying a diamond trueing tool 68. The arm 56 is provided with a handle 69 and on the hub of the arm is fixed a stop pin 10.

It is not deemed necessary to show the circuit connections for the motor but a switch to control this motor may be conveniently located at 'H on the wall ll. At 12 is a well for holding water so that if the noses of the tools get too hot during grinding they may be clipped in the water and cooled off.

In the operation of the invention there is first prepared (see Fig. 1) a master tool or master pattern such as This master is placed in the tool holder 54 and a blank for the controlling pattern 58 of greater longitudinal and lateral dimensions than the nose portion of the master form is fitted in the tool holder. The spacer 49 is next assembled on the carriage I8. The tool holder is now placed on the surface 53 and moved gradually to bring the nose of the master pattern against the block 41 while, at the same time, the controlling pattern engages the grinding face. Prior to grinding, the feed screw is turned to adjust the wheel dresser while the wheel is being dressed which fixes the proper relative position of the front face 43 of the grinding'wheel 42 relative to the abutments 40 and 41, after which the screw handle 33 is not touched. The tool holder is then swung laterally from one side to the other while the master form 6| gradually approaches block 41, until finally the nose of the controlling pattern will be ground to exact correspondence with the nose of the master tool or pattern. The step of forming a controlling pattern has then been accomplished.

As shown in Fig. 1a the large spacer box 49 may be dispensed with by providing a foot 49a attached to the bottom of the tool holder 54 as by dowel pins 491). The bottom of the foot 49a is parallel to the bottom surface of the tool holder 54 and is free to slide upon the surface 20.

To now make a duplicate of the master tool or pattern the master tool or pattern is removed from the tool holder and a work piece such as a tool blank, or a dull tool to be reground 52 is inserted. The spacer 49 is removed and the tool holder placed on the surface 20 and urged towards the grinding face until the controlling pattern 53 engages the abutment ledge 40, the latter being located as far in front of the wheel face as the surface 41 is behind it. The tool holder is now swung from side to side in forming the controlling pattern, only in this case, the controlling pattern is gradually brought against the abutment ledge 40 during the swinging operation. When the operation is completed the nose of the work piece will exactly duplicate the nose of the master tool or pattern 6| in contour and will have the clearance determined by the slope'angle e of the table and the angle of tilt f of the tool.

Obviously, a dull tool will be resharpened in exactly the samemanner as in forming a new tool bit from a blank, the dull tool being the equivalent of a blank when thus resharpened but naturally requiring less time for regrinding than the blank.

While the angle of the table is here shown as 1%" application of the bevel plate H (Fig. 8). to the surface of the table will enable other side clearance angles to be obtained, it being ob-' vious that as'many of these plates of diflerent bevels may be employed as there are tools with different side clearance angles to be ground. Pins Ha project down into holes in the table II to hold plate H in position. 7

Since in the form shown the table surface 23 is (the bevel plate H not being used) arranged with a slope of 1 viz., 1 to a plane at right angles to the wheel face and as the angle 1 between the bottom of the tool and the bottom of the tool holder is shown as 8 /z, it is obvious that the front clearance given to the tool will be 10 since at this time the tool is held in a vertical plane at right angles to the wheel face. It will also be noted that when the tool holder is swung to grind the sides of the tool, the effect of the angle 1' will have completely disappeared and the clearance applied to each side will be '1 It will also be noted that as the tool holder is gradually swung from its first mentioned position to the positions at which the sides of the tool are ground, the effect of the angle f will gradually change from its maximum of 8 to zero. Therefore, when the corner of the tool is rounded, asshown in the drawings, the clearance angle as viewed in vertical planes normal to the cutting edge at the point in question will be gradually changed from 10 when the angle 0'. in Fig. 13 is zero to 1 when the angle d becomes The same effect is produced at the right hand corner.

With a tool holder of the form shown in Fig. 7 the side clearance produced will be equal, viz., they correspond with the slope e of the table. In order to provide for a difference in the side clearance angles the use of a bevel plate 12 (Fig; 9) under thetool holder 54 is contemplated. This bevel plate is shown provided with pins 12a and 1212 which fit in suitably located holes in the bottom of tool holder 54 to properly locate the bevel plate 12 in relation thereto. Assuming that the angle of plate 12 is 1 and the plate is positioned 'so as to tilt the tool holder to the right in Fig.

7, it is clear that the clearance angle on the right 7 of the tool will be increased 1, via. to 2%..and that the clearance angle on the left will be decreased 1", via. to 5?. In other words, the relationship of the several angles mentioned is 2 n the angle through which the tool holder is tilted equals the angle e, zero side clearance will be given at one side and double clearance on the other. The tilt may of course be carried so far as to give a negative clearance on one side, if desired. It will also be noted that and x (the clearance angle at any point of a rounded corner) equals e-H cosine d (the clearance being measured in a generally vertical plane normal to the tool contour at the point in question) Another and most important characteristic of the conformation of the rounded portion of the tool produced by the method and apparatus described is that the clearance angle at any point of a rounded corner when measured in a genertime been made possible by the method and apparatus described.

Instead of using detachable bevel plates, such as II, a form of construction similar to that shown in Fig. 10 may be employed. In this form, the tool holder may consist of a base portion a formed with a bore Mb whose axis is inclined at an angle of say 855 to the bottom surface of the base. Within said bore is located the cylindrical portion c of the tool holder proper. The tool is shown as held in place by top screws 63 and 'shown in Fig. 10, or other suitable form.

asoaesa 8 variation of distribution of the side clearaace'and also for varying the angle 1.

Meanswillnowbedescribedfor grindingthe top of the tool bit and applying the proper back rake thereto. By reference to Figs. 1 and 16, it will be noted that the carriage II is formed with a groove Ila formed in its top surface 20. 'This groove extends substantially to the, grinding wheel. By referring to Figs. 1, 2, 7, and 8, it will be noted that atongue II is formed on or attached to the left side of the tool holder is. This tongue is adapted to fit in the groove Ila and to permit the sliding of the tool holder back and forth in said groove in such a position as to cause the face of the grinding wheel to grind the top face of the tool and thus apply thereto the proper rake. In the form shown in Fig. 2, the back rake is as shown and the side rake will be 0. The side rake however can be varied by usin the form of tool holder shown in Fig. 10.

In Fig. 11 is illustrated a form of construction by means of which the back rake may be readily varied. In said construction the tool holder may either be of the form shown in Fig. 7 or the one The guide tongue "a instead of being fixed to the tool holder is pivoted to the tool holder at "b and means are provided such as a screw llc threaded into a T-block 80d slidably en aged in a circular T-slot "2.. By loosening screw c the tongue 80a may be shifted to the desired position and locked in place by turning down screw Ole.

' side screws "a. The tool holder proper may be 5 turned within the said bore to the desired angle of adjustment, it being held in place as by means of a set screw 54d. As shown at Ste, suitable graduations may be applied to indicate the extent the tool holder proper has been turned relative to the base.

Figs. 15 and 16) and that the distribution of the sum of the side clearance angles may be varied by the use of bevel plates such as I! or the form of tool holder shown in Fig. 10.

- If desired, means may also be provided to vary the angle of tilt of the tool TB. This may be done by providing suitable bevel plates under the tool holder 54 or by providing a base therefor for engaging the surface 20 (and 53) said base (not shown) being pivoted to the tool holder 54 near the rear end. In that event suitable graduations would be provided to indicate the angle 1. In the alternative, a sphericalseat might be pro- Graduations as shown may be provided to facilitate setting. As the groove its is parallel to the "face of the grinding wheel the top surface of the tool will be formed parallel to the position to which tongue "a is adjusted to provide either positive or negative top rake of the desired extent. If the adjustable tongue Ila is used on a tool holder of the type shown in Fig. 10, both the back rake and the side rake may be adjusted.

In Figs. 15 and 16 is shown a slightly modified construction. In this form. instead of utilizing bevel plates such as ll (Fig. 8) in order to vary the angle of the table surface It relative to the grinding wheel the table IIB is pivoted relative to its base "A as at the point "C. This may be readily done by providing the table base "A with upstanding bosses IIA and providing the pivoted table IIB with bosses NB. Pivot screws llD threaded into the bosses IIA' provide a suitable pivot bearing for the table "3. Lock nuts IID' are preferably provided to prevent loosening of the pivot screws. Any suitable means may be provided for adjusting the table IIB about its pivots. In the form shown this is accomplished by means of a cam ss mounted for rotation with. a shaft 86 having thereon a preferably graduated adjusting knob 81 arranged in front of a suitable graduation bearing member ll attached to the table base IIA which also supports the shaft It. The cam 85 may be an eccentric or may be of spiral form such as an Archimedes spiral. It will be readily seen that as the knob 81 is rotated the front of the table will be lifted and lowered to vary the slope of the table "3.

In the position shown in Fig. 15 the table surface llB is horizontal, i. e. normal to the wheel face so that the surface ground will be cylindrlcal.

The form of tool shown in P18. 17 is similar to that shown in Figs. 12, 13, and 14. with the exception that only a small part of the front of the tool is flat, the rounded corners therefore com.

vided in the base a of Fig. 10 to provide for 1s prising a larger part of the tool profile.

The cross-sectional views shown in Figs. 18, 19, and 20, show clearly that the clearance angle a measured in generally vertical planes extending longitudinally of the tool is substantially constant at all points of the tool. This angle remains exactly constant when the table is at right angles to the wheel face. as shown in Fig. 15.

The applicant is unable to state the mathematical name of the surface generated by the above described process and apparatus as the mathematicians have apparently not as yet ascribed a name thereto. The surface may be defined as that surface which is generated by moving a straight line (generatrix) along a planar curve (directrix) while maintaining a constant angle between said straight line and a line in the plane of the curve normal to the curve at the instant point of intersection of the generatrix with the directrix. In the specific case where the slope of the tool holder supporting table is zero, the surface generated is a cylinder (although it may be a cylinder of non-circular cross-section as in Fig. 17). Furthermore, in that instance where the table is not at right angles to the wheel face the surface is conical for any part thereof where the contour of the tool (viz. the directrix) is circular. However, in that instance where the plane of the table is not at right angles to the plane of the wheel face and the directrix is a curved line other than circular, no accepted name for the surface is known. The applicant has therefore assigned thereto the name, cyclone surface, to the general form of surface generated by the apparatus and method, viz., that surface which is generated by moving a straight line (generatrix) along a planar curve (directrix) while maintaining a constant angle between said generatrix and a line inthe plane of the curve normal to the directrix at the instant point of intersection of the generatrix with the directrix.

The tool generated by my apparatus and process has a cyclone surface whose directrix plane is at such an angle to the plane of the bottom of the tool that uniform or substantially uniform relief in the direction of tool feed will be provided at all points of the tool contour. Where the tool is an in-feed or plunge-cut tool the angle of the bottom of the tool to the directrix plane is the desired angle of front relief minus the angle of slope of the table, if any. This is effected by the use of the tool holder 54 which causes the front end of the tool to be pointed up with reference to the directrix plane, viz., any plane parallel to the table surface. Likewise, where the tool is a turning tool, the angle of the bottom of the tool to the directrix plane is the desired angle of side relief minus the angle of slope of the table, if any. This may be accomplished by the use of a wedge under the tool holder as shown in Fig. 9 or by properly adjusting the tool holder of Fig. 10. The tool conformation produced is, in the absence of a known name therefor, herein termed a cyclonoid conformation.

Referring now to various other forms of tools made in accordance with the invention, reference may first be had to Figs. 21, 22, and 23. The tool IOI shown therein is a turning tool, 1. e., a lathe tool which is fed in a direction generally parallel to the axis of the work. Therefore, its clearance angle b, in the direction of feed, is greater than the front clearance angle. This is apparent from the dotted outline in Fig. 21 which indicates the bottom profile of the cutting end of the tool. Fig. 22 shows a vertical cross-section taken along the line 22-22 of Fig. 21, and Fig. 23 is a similar view taken along the line 23-21 of Fig. 21. It will be noted that although the section "-23 is taken at the curved portion of the tool nose, the

angle of clearance 22 is the same as at the straight side portion of the tool, as shown by Fig. 22.

On the general subject of clearance angles, attention is called to Figs. 31 and 32. An in-feed tool, such as a plunge-cut or facing tool, generates an Archimedes spiral on the work, in which the distance between successive turns measured radially is constant, as shown in Fig. 31. The theoretically minimum front relief angle must not be less than the spiral lead angle, which is the angle between a tangent to the spiral at any point and a line perpendicular to the radius of the work piece at that point. At any given point this angle is the one whose tangent is equal to the radial distance between successive turns of the spiral (in-feed per revolution) divided by the instantaneous circumference of the work piece at that point, or

iL a-tangent 1 Id Where a=spiral lead-angle for diameter d.

f=in-feed in inches per revolution.

d=instantaneous diameter in inches at which spiral angle is being determined.

f is constant for a given operation but d diminishes as the work progresses. Therefore, the lead angle a increases in amount as d decreases. The chart, Fig. 32, indicates how the spiral angles vary for various work diameters and various I feeds. It is clear from the chart that the spiral angle is not appreciable for diameters above one inch, except for heaviest feeds. For a feed of .050 inch per revolution, for example, the spiral angle is approximately 1 at one inch diameter. Careful attention to the spiral angle becomes important, however, when small diameters are reached. It is clear that in such tools the amount of front relief must vary in accordance with the minimum diameter to be cut thereby. In this connection attention is directed to Fig. 33 in which tools I02, I03, I04, and I05 operate upon a work piece I06 which had an original diameter of 4 inches. The tool I02 penetrates the work until a diameter of 2 inches is reached. Assuming an in-feed of .050 inch per revolution, it will be seen that the spiral angle at 2% inches is about /2. Experience has shown that it is not satisfactory to adopt the spiral angle as the proper front relief angle. To take care of variations in tool setting it has been found desirable to arbitrarily add a certain amount, say 2, to the spiral angle to achieve the most satisfactory front relief angle. Therefore, the front relief angle for tool I02 is taken at "+2=2 Tool I03 must work to a minimum diameter of inch. Therefore, as seen in Fig. 32, the spiral angle is about 1 /2 and the front relief angle is 1 +2=3 Similarly, tool I04, which operates to a minimum diameter of A inch, must have a front relief of 4+2=6, and tool I05, which must operate to a diameter of inch, must have a front relief of 13+2=15. Thus, it will be seen that tools held in the same tool holder and fed into the work the same amount per revolution must necessarily be. provided with different front relief angles to secure the most desirable results.

In longitudinally-fed lathe tools the minimum relief angle, such as the angle b in Figs. 22 and 23,

asoam 11 mustnotbeleesthantheleadangleofthehelik generated by thetool point upon thework. The leadangleofsuchahelixisdeiinedasfollowa:

when

b-ths helix angle. f feed in inches per revolution. d-ilnish tinned diameter (minimum).

Bincetheequationforthehelixangleisthesame as the equation for the angle of an Archimedes spiral,thechartofl'ig.32isapplicablealsoin determining the side relief angle in longitudinal feed (turning) tools. Knowingthe feedperrevolution and the minimum work diameter. the helix angle can readily be computed from the formula or by reference to a chart, such as Fig. 82. However,sincethereisalwaysdangerthatthetool may be tilted sideways in its holder, it is preferabletospecifyasidereliefangleseveral degrees greater than the helix angle.

By use of the above considerations it ispossible to determine the ideal minimum relief angleforanytooliftheconditlonsofitsuseare known. By utilizing the ideal minimum relief angle it is possible to give maximum strength to the cutting edge and maximum capacity for heat conduction therefrom. Itwould be futile, however, to specify such angles unless a machine were available for producing them accurately. This may be accomplished, however, by the machine showninthedrawingsanddescribedabove. This machine not only provides correct front and side relief but gradually blends the one into the other.

Fig. 24 shows an in-feed tool I" of the particular contour there shown. The effective portions of thistool are the front, the leftside, and theinclinedportiontotherightofthepoint. The right side of the tool. except at the corner, never comm into play. The essential thing is to provide the minimum relief angle in the direcnon of feed. This-may be accomplished by having the table slope sero, as shown in Fig. 15, and mthetoolinthetoolholderwithan amount of uptilt equal to the desired front clearance. 'Ihe resulting tool will, therefore, have exactly the same relief in the direction of in-' feed at all points of its eifective cutting edge.

Tool Ill of Fig. 25 is a facing tool and therefore is of the in-feed type. In view of the side reliefshown,thistoolcanbestbegroimdbysetting the work table to a certain slope, via, a slope required to give the desired side relief. V

Thetool lllofl'ig.26issgainafacingtool but as no cutting is accomplished beyond the corner, this tool may be ground by setting the table at zero and adjusting the tool holder to secure the desired amount of relief.

Fig. 27 shows an in-i'eed, cut-off tool I". Such tools require a small amount of side clearance and a greater amount of end clearance. As shown, the front edge of the tool is formed at a slight angle so as to leave the tip on the piece whichisbeingcutoif. Ingrindingsuchatool the table is preferably set at an angle of about 1% to 2 to provide the desired side clearance. and the tool holder is arranged to provide sufficient uptilt to the nose of the tool to give the desired amoimt of front clearance.

Hg. 28 shows a boringtool ill held bya boring barlll. Thistoolisessentiallyaturnlngtool and may be formed like the tool of Hg. 21 except that it is formed in reverse.

HgJDshowsaplanarorshapertooiHi. Since the feed in planars and shapers does'not occur duringthecuttingstroke,itisnotessentialthat theclearanceinthedirectionoffeedbegreater than the clearance in the'other direction. Furthermore, no consideration need be given to the spiralangieorhelixanglesincethsreisonly purely straight-line motion of the tool with respecttothework. Inviewoftheshockoccurringwhenthetoolstrikestheworkatthestart ofthecuttingstroke,itisessentialtomakethe tool edge as strong as possible by using minimum relief, thus giving maximum support to the cuttingedges. Thisfonnoftoolmaybegroundby arranging the tool holder togive zero inclination andsettingthetableatsaysflorsuchother similartothetoolshowninl'ig.21. Buehatool may desirably be ground by setting the table at zero, asshown in Fig. 15, arranging the tool holdersoastogiveanupwardtilttoth'etool equal to the amount of front clearance desired. and tilting the tool in the tool holder an additional amount to give the desired additional side clearance. This may be done by using a tool holder like the one shown in Fig. 10, or using the tool holder of Fig. 7, together witha wedge.

such as the one shown in Fig. 8.

Figs. 34 and 35 show a milling cutter having inserted cutter bits ill. Such bits are preferably ground with more clearance on the front than on the sides. This may be accomplished by setting the table to the desired amount of side clearance and arranging the tool in the holder to tilt up the desired amount of additional en clearance.

Figs. 36 and 37 show a milling cutter of the face-milling type in which one or more inserted toolbits ill areused. Thesebitsmaybeground like those showninFigs. 26, 28, or 29.

While the apparatus described above may be employed to produce the various tool forms described above, it is to be understood that a grindingmachineoftheformdisclosedinmycopending application Serial Number 433,313, filed March 4, 1942, and now Patent No. 2,381,034, granted August 7, 1945, may also be employed for this purpose.

It will be noted that the constructions shown and described serve admirably to accomplish the objects stated above. It is to be understood. however, that the various tool forms discussed above are intended merely as illustrative of the invention and not as limiting; as various other modifications thereof may be made without departing from the invention as defined by a proper interpretation of the claims which follow.

I claim:

1'. A cutting tool having front clearance and side clearance on at least one side and a connecting rounded corner, the front clearance and ,side clearance being of different degree and the clearance about said rounded corner viewed in generally vertical planes normal to the various ances being different from the front clearance and the clearances of said rounded corners viewed in generally vertical planes normal tothe Number Name I Date various parts of said rounded corner varying 1,922,178 Schultz Aug. 15, 1933 gradually from the angle of front clearance to the 2,156,354 Rozmarlch May 2, 1939 respective angle of side clearance.

WALTER MARK BURA. FOREIGN PATENTS Number Country Date REFERENCES CITED 90,924 Austria Jan. 25, 1923 The following references are of record in the HER REFER file of this patent: 0T ENCES mm Metal Cutting Tools, by De Leeuw, published UNITED STATES PA 10 by McGraw-Hill Book Co. Inc., 370 Seventh Ave., Number Name Date New York, 1922, pp. 43-55 inclusive.

553365 Redford et a1 July Mechanical Engineering, July 1930, vol. 62, No. 1,409,960 McKenzie Mar. 21, 1922 7' page ,414,520 Martin May 2, 1922 

